Poster
Mountains graphic with white diamonds on itGeoscience and Exploration

Characterization of Uranium Mineralization in the Nonacho Basin, Northwest Territories

Soapbox Wednesday, November 20, 2019 - 1:41pm to 1:48pm Theatre Lobby and Theatre 2
(Student abstract)

Author(s)

K. Landry (Presenting)
Saint Mary's University
A. Terekhova
Saint Mary's University
E. Adlakha
Saint Mary's University
J.J. Hanley
Saint Mary's University
H. Falck
Northwest Territories Geological Survey
E. Martel
Northwest Territories Geological Survey

The siliciclastic Paleoproterozoic Nonacho Basin, deposited on the western margin of the Rae craton, contains numerous uranium occurrences near its unconformable contact with crystalline basement rocks. Many of the uranium occurrences occur around MacInnis Lake, in the southwestern portion of the basin. In spite of being the subject of mineral exploration since the 1950s, there are no recent comprehensive studies on the occurrences aimed at understanding their formation (e.g., timing, physicochemical conditions, fluid and metal sources). Similarities in some geological features suggest that the Nonacho occurrences may be analogues of the world-class unconformity-type uranium deposits (UTUDs) in the Athabasca Basin, Saskatchewan. Although the available drill results from Nonacho occurrences do not suggest significant grade or tonnage, they are relevant in providing a comparative example to better understand the conditions that yield fertile intracratonic basins that can host UTUDs. Additionally, they provide insights into the metallogeny of the basin.

Field work in August 2019 examined fifteen occurrences to document mineralization, alteration styles, and host lithology, while collecting representative samples for further study. Mineralization is hosted within basement granitoid, gneiss, and gabbro, and overlying sedimentary rocks, including arkosic conglomerate and interbedded sandstone-mudstone, in fracture and high-strain zones. In many areas the host rock type is uncertain, as it appears that both the basement granitoid and overlying sedimentary package have undergone extensive alteration and weathering. Uranium mineralization occurs predominately as veinlets (~2 mm thick) in a variety of host rocks, and (at one showing) it is associated with heavy mineral layers within arkosic conglomerate. Secondary uranium mineralization, characterized by yellow staining, is prominent around primary mineralization due to remobilization of uranium during surficial weathering. Early buff yellow clay alteration pervasively replaces basement rocks proximal to the unconformity near site of mineralization. The clay may be related to low temperature paleoweathering processes. Uranium mineralization appears coeval with coarse-grained, lath-like black chlorite alteration that occurs in veinlets and stringers and crosscuts clay alteration. Chlorite veins often contain copper sulphides (e.g. chalcopyrite, bornite). Quartz-feldspar±magnetite veins (cm-dm thick) are also present at sites of uranium mineralization in both the basement and the Nonacho sedimentary package. These quartz-feldspar veins are locally saussertized, and cross-cut by black chlorite, suggesting they predate uranium mineralization but their genetic relationship is currently unclear.

By combining field data, petrographic observations, a range of complementary geochemical and microanalytical techniques (e.g., bulk-rock geochemistry, fluid inclusion petrography and microthermometry, laser ablation inductively-coupled plasma mass spectrometry and radiometric age dating), this project aims to: (i) characterize the styles of uranium mineralization, noting similarities and differences between their structure, mineralogy, mineral chemistry and paragenesis of mineralization and associated alteration; (ii) constrain the absolute age of mineralization, (iii) determine sources for metals and fluids, and (iv) classify the mineralization type (e.g., UTUDs). This information will add to the current understanding of the metallogeny, fluid history, and structural evolution of the Nonacho Basin. Additionally, it will provide constraints on the conditions required for fertile and infertile intracratonic basins with respect to UTUDs.